Specifications

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Appendix A Glossary
output has a PFC of 1.0. In practice, high-quality
power supplies and UPS units have PFCs in the
90%–97% range (.90–.97 PFC).
power management Systems used initially in
mobile computers (and now also used in desktop
systems) to decrease power consumption by turn-
ing off or slowing down devices during periods of
inactivity. See also APM.
power supply An electrical/electronic circuit
that supplies all operating voltage and current to
the computer system.
PPGA (plastic pin grid array) A chip-
packaging form factor used by Intel as an alterna-
tive to traditional ceramic packaging.
PPP (Point-to-Point Protocol) A protocol that
enables a computer to use the Internet with a stan-
dard telephone line and high-speed modem. PPP
has largely replaced the Serial Line Internet
Protocol (SLIP) because it supports line sharing and
error detection.
PPPoE (Point-to-Point Protocol over
Ethernet) A specification for connecting to the
Internet, used primarily on DSL connections.
precompensation A data write modification
required by some older drives on the inner cylin-
ders to compensate for the higher density of data
on the (smaller) inner cylinders.
Presentation Layer See OSI.
primary partition An ordinary, single-volume
bootable partition. See also extended partition.
printer A device that records information visu-
ally on paper or other material.
Private Branch Exchange (PBX) A private
telephone network used within an organization.
processor See microprocessor.
processor speed The clock rate at which a
microprocessor processes data. A typical Pentium 4
processor, for example, operates at 2GHz (2 billion
cycles per second).
program A set of instructions or steps telling the
computer how to handle a problem or task.
Programmable Logic Controller (PLC) An
electronic device that can be programmed to con-
trol a process or machine operation.
PROM (programmable read-only memory)
A type of memory chip that can be programmed to
store information permanently—information that
can’t be erased. Also referred to as OTP for one-time
programmable.
proprietary Anything invented by one com-
pany and uses components available from only
that one company. Especially applies to cases in
which the inventing company goes to lengths to
hide the specifications of the new invention or to
prevent other manufacturers from making similar
or compatible items. The opposite of standard or
open architecture. Computers with nonstandard
components that are available from only the origi-
nal manufacturer, such as Apple Macintosh sys-
tems, are known as proprietary.
protected mode A mode available in all
Intel and compatible processors except the first-
generation 8086 and 8088. In this mode, memory
addressing is extended beyond the 1MB limits of
the 8088 and real mode and restricted protection
levels can be set to trap software crashes and con-
trol the system.
protocol A system of rules and procedures gov-
erning communications between two or more
devices. Protocols vary, but communicating devices
must follow the same protocol to exchange data.
The data format, readiness to receive or send, error
detection, and error correction are some of the
operations that can be defined in protocols.
proxy server A computer that acts as a gateway
between the computers on a network and the
Internet and also provides page caching and
optional content filtering and firewall services to
the network. Some home network software solu-
tions for Internet sharing, such as WinProxy, use a
proxy server.
PS/2 mouse A mouse designed to plug into a
dedicated mouse port (a round, 6-pin DIN connec-
tor) on the motherboard, rather than plugging into
a serial port. The name comes from the fact that
this port was first introduced on the IBM PS/2
systems.
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